Fluid actuators, either hydraulic or pneumatic, are frequently employed for moving components of machinery from one position to another. Normally actuators are of the type in which fluid pressure is applied to move a piston in a cylinder. Two position actuators are common wherein fluid pressure may be applied to either end of the cylinder to positively move a piston in one direction or the other.
The present invention is directed towards a type of actuator having three positions, that is, wherein fluid pressure may be applied to move a piston in a cylinder in either direction relative to the cylinder and including an intermediate position in which the piston is normally retained when not actuated by fluid pressure. Three position actuators are known in industry, however, the three position actuator described herein has the characteristic of positively returning the piston to a preselected intermediate position when fluid pressure is removed.
Important characteristics of the three position actuator of this invention are: (a) variable stroke lengths from the intermediate position may be selected; and (b) no fluid pressure is required to retain the piston in the intermediate position.
It is therefore an object of this invention to provide an improved fluid powered actuator. More particularly, an object of the invention is to provide a three position fluid powered actuator including means of positively returning a piston to a preselected intermediate position.
Still more particularly, an object of this invention is to provide a three position fluid powered actuator including improved and simplified means of selecting the variable stroke length from the intermediate position of the piston.
These general objects as well as other and more specific objects of the invention will be fulfilled in the following description and claims, taken in conjunction with the attached drawings.